The present invention relates to vent valve devices, and particularly to such vent valve devices that are adapted to propagate an emergency rate of reduction of pressure in the brake pipe on the locomotive of a railway train.
A typical locomotive brake valve device, such as the well-known 26C Brake Valves, incorporates a vent valve that is operated manually by movement of the brake valve handle to emergency position, thereby initiating an emergency rate of reduction of the locomotive brake pipe pressure. A typical locomotive brake system may also include an E-3 Brake Application Valve that is operated independently of the locomotive brake valve, and provides a means of initiating an emergency venting of brake pipe pressure at a location remote from the locomotive brake valve. In addition, an independent vent valve device, such as the well-known #8 Vent Valve, is employed on a locomotive to in turn vent the locomotive brake pipe in response to an emergency rate of reduction of the brake pipe pressure initiated by the locomotive brake valve or by the E-3 Brake Application Valve in order to propagate the emergency venting of brake pipe pressure through the locomotive to a trailing locomotive and/or to the cars of a railway train. It is well-known in the railway braking art that Control Valves on these locomotives and/or cars are rate-sensitive and, accordingly, respond to an emergency reduction of brake pipe pressure to effect an emergency application of the locomotive and/or car brakes.
All of the above-mentioned locomotive valves are conventional components of a locomotive brake system and are manufactured by the Westinghouse Air Brake Company.
As mentioned above, the #8 Vent Valve propagates an emergency brake application by venting brake pipe pressure in response to an emergency rate of reduction of the brake pipe pressure. When the brake pipe pressure is reduced at a sufficiently rapid rate to establish a predetermined differential pressure between air stored in a control chamber (typically referred to as the quick action chamber) and air in the brake pipe, an actuating piston subject to this predetermined pressure differential, on opposite sides thereof, operates to open a vent valve via which the brake pipe air is vented to atmosphere substantially unrestricted. Proper tuning, by appropriate selection of chokes between the control chamber and the brake pipe pressures, establishes the predetermined pressure differential required to operate the actuating piston when an emergency rate of reduction occurs.
It will be appreciated, however, that in order to provide stability during service braking, the emergency rate of brake pipe reduction at which the #8 Vent Valve is set to operate must be significantly greater than the maximum service rate, to thereby prevent inadvertent and undesired emergency brake applications from occurring, due to brake pipe pressure fluctuations, for example. For this reason, the #8 Vent Valve is not entirely positive in its operation.